1. Field of the Invention
Conventionally, for multiple molding using a plurality of nest molds put in one mold base, a plurality of insert holes corresponding to the number of nest molds to be inserted are bored on the mold base, and the nest molds put in the insert holes are fixed by suitable fixing means. The fixation of the nest mold in the insert hole is effected by pressing the nest mold by a clamp piece of a clamping device to bring two faces of the nest mold into contact with two faces of the insert hole as the reference faces.
2. Description of the Background Art
FIG. 18 shows an example of a conventional molding mold of this type.
A movable mold 10, an intermediate mold 11, and a stationary mold 12 are provided. Each of the movable mold 10 and the intermediate mold 11 contains, for example, four inserted and fixed nest molds which, upon mold closure, form molding cavities 13 (only one nest mold being shown in the figure). As seen in the figure, on each mold base a plurality of insert holes are bored, each for each nest mold, corresponding to the number of the nest molds needed. Each nest mold 14 is inserted in its corresponding insert hole 23 and fixed separately by a fixing means such as a clamping device (not shown). On each nest mold 14, a runner hole 15 is provided which serves to introduce resin into the cavity 13. On the stationary mold 12, a hot runner block 17 is provided which serves to keep the resin injected through a nozzle 16 melted and hot. The front end of the hot runner block 17 extends to the middle of the back face of the intermediate mold 11. On a receiver plate 18 fixed on the back face of the intermediate mold 11 for holding the nest mold 14, there are radially engraved a runner groove 19 which connects the front end of the hot runner block 15 to each of the runner holes 17 so as to guide the resin from the hot runner block 17 to the inside of each cavity 13. A runner stripper plate 20 may move to and from the stationary mold 12 within a range of a short stroke relative to the stationary mold base 21. On this runner stripper plate 20, a runner lock pin 22 is provided which projects from the stationary mold base 21 and is provided at its tip with an undercut.
For molding, the mold is first closed, and then melted resin is introduced into the cavity 13 from the nozzle 16 through the hot runner block 17, runner groove 19, and runner hole 15. As the mold is opened after molding, the contact between the intermediate mold 11 and the runner stripper plate 20 is opened, the runner branch is cut off at the molded product at the gate, and the undercut of the runner lock pin 22 holds the runner branch adhering to the side of the runner stripper plate 20. Subsequently, the contact between the movable mold 10 and the intermediate mold 11 is opened, and the molded product is exposed and ejected by a suitable ejector pin (not shown). The runner branch falls when the contact between the runner stripper plate 20 and the stationary mold base 21 is opened.
These conventional molding molds have several problems including the need for a plurality of insert holes 23 which are bored on the mold base according to the number of nest molds. Boring of these insert holes complicates the processing of the mold base and increases the production cost. Also, some device for fixing the nest mold 14 in an insert hole needs to be provided on each insert hole 23, which further complicates the molding mold and makes the replacement of nest mold 14 timeconsuming.
Another problem involves the use of plural insert holes 23 which are required to be formed at regular intervals. These holes cause the size of the mold base to become larger and necessarily enlarge the injection molding machine on which the molding mold is attached.
The runner branch is formed as a long cold runner in accordance with the runner groove 19 radially extending from the front end of the hot runner block and this design results in material waste. Especially when the molded product is small, the ratio of runner branch to product is so large as to make the material waste serious.
A further problem arises when the number of the nest molds to be actually adopted is, for example, 3 which is less than the prescribed number. A substitute nest mold having neither cavity nor runner hole provided is then applied in the empty space of the intermediate mold 11. In this case, the same runner branch is formed in the runner groove 19 extending to the substitute mold, resulting also in material waste.
A conceivable way of decreasing the cold runner in volume to cut down the material waste is to extend the hot runner block to a position close to each nest mold, thereby minimizing the runner branch to be formed.
A material-saving way applicable to the case of using a substitute nest mold is to design the contact face of the substitute nest mold to be close to the resin outlet of the hot runner block, thereby eliminating the formation of the runner branch for the substitute nest mold.
However, it has been found that, when the resin outlet of the hot runner block is closed by the substitute nest mold, the resin in the hot runner block is heated to such a high temperature as to be decomposed or deteriorated, resulting in an unfavorable effect which prevents subsequent molding.